1. Field of the Invention
This invention relates to a solid-state imaging device and a driving method for a solid-state imaging device as well as an electronic apparatus, and more particular to a technique for reducing generation of noise in a solid-state imaging device and a driving method for a solid-state imaging device as well as an electronic apparatus.
2. Description of the Related Art
A popular image sensor of the CMOS (Complementary Metal Oxide Semiconductor) type includes a mechanism for sequentially scanning a pixel array, in which pixels are arrayed two-dimensionally, for each pixel row to carry out reading out. This row-sequential scanning generates a displacement in time among accumulation periods with regard to different pixel rows and gives rise to occurrence of a phenomenon called focal plane distortion that a picked up image upon imaging of a moving imaging object is distorted.
In imaging applications to an imaging object moving at a high speed which cannot permit such image distortion or in sensing applications which require simultaneity of picked up images, some CMOS image sensor carries out driving for establishing simultaneity of the accumulation periods of the pixel array. In particular, for the driving described, accumulation over an overall area of the pixel array is started simultaneously by simultaneous resetting driving for all rows of photodiodes (PD) in the pixel array. Then, the accumulation over the overall area is ended by simultaneous transfer driving for all rows to charge accumulation sections such as floating diffusions (FD).
Among such CMOS image sensors, a CMOS image sensor is known and disclosed, for example, in Japanese Patent Laid-Open No. 2004-140149 (hereinafter referred to as Patent Document 1) wherein, in order to provide a degree of freedom in time between a row-sequential reading out period and an exposure period, a simultaneous charge discharging unit or overflow gate is provided for a photodiode (PD). The CMOS image sensor of the Patent Document 1 mentioned above carries out an operation of opening the overflow gates simultaneously for all rows to discharge charge of the photodiodes intermediately within a row-sequential reading out period. The CMOS image sensor further carries out another operation of stopping the discharging operation at a point of time of a predetermined row, that is, keeping the overflow gates closed simultaneously to start exposure of the photodiodes simultaneously and then continue the exposure. Then, at the top of a next frame period, the exposure is ended by simultaneous transfer driving for all rows to the charge accumulation sections such as floating diffusions to carry out sequential reading out operation of the signals of the photodiodes. By the sequence of operations, starting of the exposure period can be set to a free row timing including a period for sequential reading out in a unit of a row to achieve improvement of the degree of freedom in exposure time.